In the manufacturing industry of printed wiring boards, photosensitive elements produced by using a photosensitive resin composition, a support and a protective film have been widely used as the resist materials in etching, plating or the like.
Printed wiring boards are produced by laminating a photosensitive element on a copper substrate, exposing it with patterned light, removing unexposed areas with a developer, carrying out etching or plating to form circuit patterns, and then peeling off the cured areas from the substrate.
Developers mainly used to remove the unexposed areas are of alkali development type, such as a sodium carbonate solution. Developers are used repeatedly so long as they substantially retain the ability of dissolving photosensitive resin composition layers, and photosensitive resin compositions are dissolved or dispersed in the developers during development.
With the recent increase in the density of printed wiring boards, the contact area between copper substrates and patterned photosensitive resin composition layers has been reduced, requiring photosensitive elements which exhibit excellent adhesiveness, resolution, tenting reliability and chemical resistance in etching or plating step.
Also there is the problem of the aggregation of the photosensitive resin composition dissolved or dispersed in developers. When the developer is sprayed again with a pump or the like, the aggregates dispersed in the developers adhere onto developed printed wiring boards, causing undesirable defects during the following etching or plating step. To prevent such defects, photosensitive resin compositions require good dispersion stability in developers.
As to resists improved in chemical resistance, for example, resists containing copolymers of styrene monomers are disclosed in Japanese Patent Application Examined Publication Nos. 55-38961 (1980) and 54-25957 (1979), Japanese Patent Application Unexamined Publication Nos. 2289607 (1990), 4-347859 (1992) and 4-285960 (1992). However, the minimum development time of the resists is so long as to reduce resolution.
To improve chemical resistance, the use of photo-polymerizable compounds having isocyanurate rings is proposed in Japanese Patent Application Unexamined Publication Nos. 60-77844 (1985), 62-290705 (1987), 60-14212 (1985), 59-222480 (1984), 1-14190 (1989), 57-55914 (1982), 5-216224 (1993) and 5-273754 (1993), which however involves the problem that the cured film is hard and brittle.
As to photosensitive resin compositions with good tenting reliability, a photosensitive resin composition using vinylurethane compounds is disclosed in Japanese Patent Application Unexamined Publication No. 7-128851 (1995). However, with the recent increase in the density and accuracy of printed wiring boards, the requirement for high resolution has become yearly strict, and the addition of vinylurethane compounds alone cannot improve the resolution of the photosensitive resin composition. This is assumed to be caused by the poor developability of the isocyanate residues having urethane bonds.
In Japanese Patent Application Unexamined Publication No. 8-179503 (1996) is disclosed that photosensitive resin compositions having a low biologically chemical oxygen demand and a low chemical oxygen demand and being less apt to aggregate in developers are obtainable by using, as an ethylenically unsaturated compound, a specific urethane compound having in its molecule blocked ethylenoxy or propylenoxy groups. The photosensitive resin compositions however involve the defects of low adhesiveness on overdevelopment and insufficient reduction in minimum development time.
In Japanese Patent Application Unexamined Publication No. 5-232699 (1993) disclosed are photosensitive resin compositions containing acrylate compounds, which, having extremely hydrophilic polyalkylene glycol chains, are excellent in developability and resolution. The photosensitive resin compositions involve problems in that those with only polyethylene glycol chains suffer from defective resist shapes, jagged etched-lines or the like, while those with only polypropylene glycol chains tend to separate to scum in alkaline developers, and if the scum adheres to substrates, it causes short circuit or disconnection.